This invention relates generally to cryogenic rectification and is particularly useful for carrying out cryogenic air separation.
Cryogenic rectification, such as the cryogenic rectification of feed air, requires the provision of refrigeration to drive the separation. Generally such refrigeration is provided by the turboexpansion of a process stream, such as, for example, a portion of the feed air. While this conventional practice is effective, it is limiting because any change in the requisite amount of refrigeration inherently affects the operation of the overall process. It is therefor desirable to have a cryogenic rectification system wherein the provision of the requisite refrigeration is independent of the flow of process streams for the system.
One method for providing refrigeration for a cryogenic rectification system which is independent of the flow of internal system process streams is to provide the requisite refrigeration in the form of cryogenic liquid brought into the system. Unfortunately such a procedure is very costly.
Accordingly it is an object of this invention to provide an improved cryogenic rectification system wherein the provision of at least some of the refrigeration for the separation is independent of the turboexpansion of process streams and does not require the provision of exogenous cryogenic liquid to the system.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for carrying out cryogenic rectification comprising:
(A) passing feed into a cryogenic rectification plant comprising at least one column;
(B) magnetizing a bed of magnetizable particles to heat the magnetizable particles, heating refrigerator gas by contacting the refrigerator gas with the magnetized particles, cooling the heated refrigerator gas, demagnetizing the bed of magnetizable particles, and passing cooled refrigerator gas in contact with the demagnetized particles to produce cooled refrigerator gas containing refrigeration;
(C) passing refrigeration from the refrigerator gas into the cryogenic rectification plant; and
(D) separating the feed by cryogenic rectification within the cryogenic rectification plant using refrigeration from the refrigerator gas.
Another aspect of the invention is:
Apparatus for carrying out cryogenic rectification comprising:
(A) a cryogenic rectification plant comprising at least one column and means for passing feed into the cryogenic rectification plant;
(B) a magnetic refrigerator comprising a bed of magnetizable particles, means for magnetizing and demagnetizing the bed of magnetizable particles, and means for passing refrigerator gas through the bed of magnetizable particles;
(C) means for passing refrigeration from the magnetic refrigerator into the cryogenic rectification plant; and
(D) means for recovering product from the cryogenic rectification plant.
As used herein the term xe2x80x9ccolumnxe2x80x9d means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. 
The term xe2x80x9cdouble columnxe2x80x9d is used to mean a higher pressure column having its upper portion in heat exchange relation with the lower portion of a lower pressure column. A further discussion of double columns appears in Ruheman xe2x80x9cThe Separation of Gasesxe2x80x9d, Oxford University Press, 1949, Chapter VII, Commercial Air Separation.
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Distillation is the separation process whereby heating of a liquid mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases can be adiabatic or nonadiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cproduct nitrogenxe2x80x9d means a fluid having a nitrogen concentration of at least 95 mole percent.
As used herein the term xe2x80x9cproduct oxygenxe2x80x9d means a fluid having an oxygen concentration of at least 85 mole percent.
As used herein the term xe2x80x9cproduct argonxe2x80x9d means a fluid having an argon concentration of at least 90 mole percent.
As used herein the term xe2x80x9cfeed airxe2x80x9d means a mixture comprising primarily oxygen, nitrogen and argon, such as ambient air.
As used herein the terms xe2x80x9cupper portionxe2x80x9d and xe2x80x9clower portionxe2x80x9d mean those sections of a column respectively above and below the mid point of the column.